Mold and aligner with features showing cut line

ABSTRACT

Embodiments relate to adding customized cut line information to a shell that is to be formed over mold of a dental arch. In one embodiment, a processing device generates or receives a digital three-dimensional model of a mold for a dental arch of a patient. The processing device determines a cut line for a shell that is to be formed over the mold for the dental arch of the patient. The processing device then supplements the digital three-dimensional model by adding an auxiliary structure to the digital three-dimensional model, wherein the auxiliary structure comprises at least one of an elevation or a depression that extends along the cut line in the digital three-dimensional model, wherein the auxiliary structure will cause the shell formed over the mold to have an impression of the auxiliary structure that identifies the cut line.

RELATED APPLICATIONS

This patent application is a continuation application of U.S. patentapplication Ser. No. 15/730,626, filed Oct. 11, 2017, which claims thebenefit under 35 U.S.C. § 119(e) of U.S. Provisional Application No.62/414,361, filed Oct. 28, 2016, both of which are herein incorporatedby reference.

TECHNICAL FIELD

Embodiments of the present invention relate to the field of rapidprototyping molds and, in particular, to a mold having cut line featuresthat imprint a material thermoformed over the mold with cut linemarkings that show where to cut the material after thermoforming.Embodiments additionally relate to an orthodontic aligner with cut linemarkings that is either directly manufactured or manufactured bythermoforming a sheet of material over a mold having the cut linefeatures.

BACKGROUND

For some applications, shells are formed around molds to achieve anegative of the mold. The shells are then removed from the molds to befurther used for various applications. One example application in whicha shell is formed around a mold and then later used is correctivedentistry or orthodontic treatment. In such an application, the mold isof a dental arch for a patient and the shell is an aligner to be usedfor aligning one or more teeth of the patient.

Molds may be formed using rapid prototyping equipment such as 3Dprinters, which may manufacture the molds using additive manufacturingtechniques (e.g., stereolithography) or subtractive manufacturingtechniques (e.g., milling). The aligners may then be formed over themolds using thermoforming equipment. Once the aligner is formed, acomputer controlled 4-axis or 5-axis trimming machine (e.g., a lasertrimming machine or a mill) is typically used to trim the aligner alonga cut line. The trimming machine uses electronic data that identifiesthe cut line to trim the aligner. The cut line information is nottransferred to either the molds or the aligners.

Rapid prototyping equipment and thermoforming equipment is compactequipment that may be possessed by laboratories, dentist offices,orthodontics offices, and so forth. However, a trimming machine such asa laser trimming machine or a mill trimming machine are large expensivemachines that are not generally owned by laboratories, dentist officesor orthodontics offices. Accordingly, such laboratories, dentistoffices, orthodontics offices, etc. may manually trim the aligner afterit is thermoformed over the mold in a manner that might compromise theefficacy of the appliance or the comfort of the patient.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings.

FIG. 1A illustrates a flow diagram for a method of fabricating a moldwith features that imprint shells with cut line markings, in accordancewith one embodiment.

FIG. 1B illustrates a flow diagram for a method of trimming a shellusing cut line markings imprinted in the shell, in accordance with oneembodiment.

FIG. 2A illustrates a flow diagram for a method of fabricating a moldwith cut line markings for a shell formed over the mold, in accordancewith one embodiment.

FIG. 2B illustrates a flow diagram for a method of trimming a shellusing cut line markings in a mold over which the shell is formed, inaccordance with one embodiment.

FIG. 3 illustrates a flow diagram for a method of directly fabricatingan aligner or other shell with cut line markings, in accordance with oneembodiment.

FIG. 4A illustrates a mold of a dental arch with markings that show acut line for a shell formed over the mold, in accordance with oneembodiment.

FIG. 4B illustrates a mold of a dental arch with markings that show acut line for a shell formed over the mold, in accordance with anotherembodiment.

FIG. 4C illustrates a mold of a dental arch with features that willcause a shell formed over the mold to have cut line markings, inaccordance with one embodiment.

FIG. 4D illustrates a mold of a dental arch with features that willcause a shell formed over the mold to have cut line markings, inaccordance with another embodiment.

FIG. 4E illustrates a mold of a dental arch with features that willcause a shell formed over the mold to have cut line markings, inaccordance with another embodiment.

FIG. 5 illustrates an example orthodontic aligner worn by a person.

FIG. 6 illustrates a block diagram of an example computing device, inaccordance with embodiments of the present invention.

DETAILED DESCRIPTION

Described herein are embodiments covering computer aided drafting (CAD)and computer aided manufacturing (CAM) systems that embed cut lineinformation for shells such as orthodontic aligners into digital modelsof molds that are used to form the shells and/or into digital models ofthe shells. Traditionally aligners are trimmed by hand and there is notrim line information provided to facilitate trimming of the aligners.In some large production facilities, trimming is performed by machinesusing a customized trim line (also referred to as a cut line) determinedby a large production facility. Embodiments described herein enable alarge production facility to transfer the customized trim lineinformation to smaller production facilities. For example,traditionally, a large production facility generates a digital model fora mold, manufactures the mold from the digital model, forms a shell overthe mold, and then trims the shell along a cut line with a computercontrolled mill or computer controlled laser cutting machine using anelectronic file that contains information for the cut line. However, insome instances it can be useful for a third party such as a dentallaboratory, clinician office or other smaller production facility tomanufacture a shell based on a digital model received from an entity(e.g., large production facility) that generates the digital model. Forexample, an orthodontist or laboratory may want the ability to quicklyreplace a shell that is lost by a patient. The third party may receivethe digital model of the mold, use the digital model and a rapidprototyping machine to form the mold, and then form the shell over themold. Such a third party may lack a computer controlled mill machine ora laser cutting machine. Accordingly, a technician for the third partylikely will manually trim the shell.

For shells such as orthodontic aligners, orthodontic retainers andorthodontic splints, the trimming of the shell is important to theefficacy of the shell for its intended purpose (e.g., aligning,retaining or positioning one or more teeth of a patient) as well as thefit of the shell on a patient's dental arch. For example, if too much ofthe shell is trimmed, then the shell may lose rigidity and an ability ofthe shell to exert force on a patient's teeth may be compromised. On theother hand, if too little of the shell is trimmed, then portions of theshell may impinge on a patient's gums and cause discomfort, swelling,and/or other dental issues. Additionally, if too little of the shell istrimmed at a location, then the shell may be too rigid at that location.Often, the optimal cut line is away from the gum line (also referred toas the gingival line) in some regions and on the gum line in otherregions. For example, it may be desirable in some instances for the cutline to be away from the gum line (e.g., not touching the gum) where theshell will touch a tooth and on the gum line (e.g., touching the gum) inthe interproximal regions between teeth. Accordingly, it is importantthat the shell be trimmed along a predetermined cut line. However, itcan be very challenging for a technician to manually trim a shell alongthe intended cut line because there are not indicators of that cut lineon the shell being trimmed.

A shell may additionally have multiple cut lines. A first or primary cutline may control a distance between an edge of the shell and a gum lineof a patient. Additional cut lines may be for cutting slots, holes, orother shapes in the shell. For example, an additional cut line may befor removal of an occlusal surface of the shell, an additional surfaceof the shell, or a portion of the shell that, when removed, causes ahook to be formed that is usable with an elastic. This can furtherincrease a difficulty of manually trimming the shell.

Accordingly, embodiments cover techniques for transferring the cut lineinformation to the mold and/or to the shell that is to be trimmed. Bytransferring the cut line information to the shell that is to betrimmed, a technician is provided a guide for trimming the shell. Thiscan greatly increase the accuracy for trimming the shell along thepredetermined cut line.

In one embodiment, a cut line is determined for the shell. A processingdevice determines one or more markings for the shell that will mark thecut line. The processing device determines one or more features to addto a mold over which the shell will be formed that will cause the shellto have the one or more markings. The processing device then generates adigital model of the mold, the digital model comprising the one or morefeatures, wherein the digital model is usable to manufacture the moldhaving the one or more features. When a third party receives the digitalmodel, they may use it to manufacture the mold, and may then form theshell over the mold. The mold and/or the shell may include markings thatindicate the correct cut line. A technician may then manually trim theshell along the intended cut line using the included markings. As aresult, the finished product of the shell will fit a patient well andwill function as it was designed to.

In another embodiment, a cut line is determined for a shell that is tobe formed over a mold of a dental arch. A processing device determinesone or more markings to add to the mold over which the shell will beformed that will cause the cut line to be visible while the shell is onthe mold. The processing device then generates a digital model of themold, the digital model comprising the one or more markings. The digitalmodel is usable to manufacture the mold having the one or more markings.A technician may then manually trim the shell along the intended cutline while the shell is on the mold using the included markings in themold. As a result, the finished product of the shell will fit a patientwell and will function as it was designed to.

In another embodiment, one or multiple cut lines may be determined. Somecut line markings may ultimately be transferred to a shell that isformed. Other cut line markings may be in the mold, but may not betransferred to the shell.

In one embodiment, a processing device determines a cut line for anorthodontic aligner that is to be used for aligning one or more teeth ofa patient. The processing device determines one or more markings orelements to add to the orthodontic aligner that will mark the cut line.The processing device then generates (or updates) a digital model of thealigner, the digital model comprising the one or more markings orelements, wherein the digital model is usable to manufacture thealigner.

Some embodiments are discussed herein with reference to orthodonticaligners (also referred to simply as aligners). However, embodimentsalso extend to other types of shells formed over molds, such asorthodontic retainers, orthodontic splints, sleep appliances for mouthinsertion (e.g., for minimizing snoring, sleep apnea, etc.) and/orshells for non-dental applications. Accordingly, it should be understoodthat embodiments herein that refer to aligners also apply to other typesof shells. For example, the principles, features and methods discussedmay be applied to any application or process in which it is useful totransfer cut line information to shells that are form fitting devicessuch as eye glass frames, contact or glass lenses, hearing aids orplugs, artificial knee caps, prosthetic limbs and devices, orthopedicinserts, as well as protective equipment such as knee guards, athleticcups, or elbow, chin, and shin guards and other like athletic/protectivedevices.

Referring now to the figures, FIG. 1A illustrates a flow diagram for amethod 100 of fabricating a mold with features that imprint shells suchas aligners with cut line markings, in accordance with one embodiment.One or more operations of method 100 are performed by processing logicof a computing device. The processing logic may include hardware (e.g.,circuitry, dedicated logic, programmable logic, microcode, etc.),software (e.g., instructions executed by a processing device), firmware,or a combination thereof. For example, one or more operations of method100 may be performed by a processing device executing a computer aideddrafting (CAD) program or module such as model generator 650 of FIG. 6 .

At block 102 of method 100, a shape of a dental arch for a patient at atreatment stage is determined based on a treatment plan. In the exampleof orthodontics, the treatment plan may be generated based on anintraoral scan of a dental arch to be modeled. The intraoral scan of thepatient's dental arch may be performed to generate a three dimensional(3D) virtual model of the patient's dental arch. For example, a fullscan of the mandibular and/or maxillary arches of a patient may beperformed to generate 3D virtual models thereof. The intraoral scan maybe performed by creating multiple overlapping intraoral images fromdifferent scanning stations and then stitching together the intraoralimages to provide a composite 3D virtual model. In other applications,virtual 3D models may also be generated based on scans of an object tobe modeled or based on use of computer aided drafting techniques (e.g.,to design the virtual 3D mold). Alternatively, an initial negative moldmay be generated from an actual object to be modeled. The negative moldmay then be scanned to determine a shape of a positive mold that will beproduced.

Once the virtual 3D model of the patient's dental arch is generated, adental practitioner may determine a desired treatment outcome, whichincludes final positions and orientations for the patient's teeth.Processing logic may then determine a number of treatment stages tocause the teeth to progress from starting positions and orientations tothe target final positions and orientations. The shape of the finalvirtual 3D model and each intermediate virtual 3D model may bedetermined by computing the progression of tooth movement throughoutorthodontic treatment from initial tooth placement and orientation tofinal corrected tooth placement and orientation. For each treatmentstage, a separate virtual 3D model of the patient's dental arch at thattreatment stage may be generated. The shape of each virtual 3D modelwill be different. The original virtual 3D model, the final virtual 3Dmodel and each intermediate virtual 3D model is unique and customized tothe patient.

Accordingly, multiple different virtual 3D models may be generated for asingle patient. A first virtual 3D model may be a unique model of apatient's dental arch and/or teeth as they presently exist, and a finalvirtual 3D model may be a model of the patient's dental arch and/orteeth after correction of one or more teeth and/or a jaw. Multipleintermediate virtual 3D models may be modeled, each of which may beincrementally different from previous virtual 3D models.

Each virtual 3D model of a patient's dental arch may be used to generatea unique customized mold of the dental arch at a particular stage oftreatment. The shape of the mold may be at least in part based on theshape of the virtual 3D model for that treatment stage. Aligners may beformed from each mold to provide forces to move the patient's teeth. Theshape of each aligner is unique and customized for a particular patientand a particular treatment stage. In an example, the aligners can bepressure formed or thermoformed over the molds. Each mold may be used tofabricate an aligner that will apply forces to the patient's teeth at aparticular stage of the orthodontic treatment. The aligners each haveteeth-receiving cavities that receive and resiliently reposition theteeth in accordance with a particular treatment stage.

At block 105, processing logic determines a cut line for the aligner.This determination may be made based on the virtual 3D model of thedental arch at a particular treatment stage, based on a virtual 3D modelof the aligner to be formed over the dental arch, or a combination of avirtual 3D model of the dental arch and a virtual 3D model of thealigner. Each aligner has a unique shape that is customized to fit overa patient's dental arch at a particular stage of orthodontic treatment.After an aligner is formed over a mold for a treatment stage, thataligner is subsequently trimmed along a cut line (also referred to as atrim line). The cut line may be a gingival cut line that represents aninterface between an aligner and a patient's gingiva. The cut linecontrols a distance between an edge of the aligner and a gum line orgingival surface of a patient. Each patient has a unique dental archwith unique gingiva. Accordingly, the shape and position of the cut linewill be unique and customized for each patient and for each stage oftreatment. The location and shape of the cut line can be important tothe functionality of the aligner (e.g., an ability of the aligner toapply desired forces to a patient's teeth) as well as the fit andcomfort of the aligner. In one embodiment, the cut line covers thebuccal, lingual and palatal regions of the aligner.

In accordance with one embodiment, the cut line is determined by firstdefining initial gingival curves along a line around a tooth (LAT) of apatient's dental arch from a virtual 3D model (also referred to as adigital model) of the patient's dental arch for a treatment stage. Thegingival curves may include interproximal areas between adjacent teethof a patient as well as areas of interface between the teeth and thegums. The initially defined gingival curves may be replaced with amodified dynamic curve that represents the cut line.

Defining the initial gingival curves along a line around a tooth (LAT)can be suitably conducted by various conventional processes. Forexample, such generation of gingival curves can include any conventionalcomputational orthodontics methodology or process for identification ofgingival curves. In one example, the initial gingival curves can begenerated by use of the Hermite-Spline process. In general, the Hermiteform of a cubic polynomial curve segment is determined by constraints onendpoints P₁ and P₄ and tangent vectors at endpoints R₁ and R₄. TheHermit curve can be written in the following form:Q(s)=(2s ³−3s ²+1)P ₁+(−2s ³+3s ²)P ₄+(s ³−2s ² +s)R ₁+(s ³ −s ²)R ₄;s[0,1]  (1)Equation (1) can be rewritten as:Q(s)=F ₁(s)P ₁ +F ₂(s)P ₄ +F ₃(s)R ₁ +F ₄(s)R ₄;  (2)Wherein equation (2) is the geometric form of the Hermite-Spline Curve,the vectors P₁, P₄, R₁, R₄ are the geometric coefficients, and the Fterms are Hermite basis functions.

A gingival surface is defined by gingival curves on all teeth and a baseline, with the base line being obtained from a digital model of thepatient's dental arch. Thus, with a plurality of gingival curves andbase line, a Hermite surface patch that represents the gingival surfacecan be generated.

Rather than having a cut line that causes a sharp point or other narrowregion in the interproximal areas between teeth that can cause weakeningof the aligner material during use, the initial gingival curves may bereplaced with a cut line that has been modified from the initialgingival curves. The cut line can be generated to replace the initialgingival curves by initially obtaining a plurality of sample points froma pair of gingival curve portions residing on each side of aninterproximal area. The sample points are then converted into pointlists with associated geometric information (e.g., into the AmsterdamDentistry Functional (ADF) format or other like data formats). Samplepoints may be suitably selected proximate the inner region between twoteeth, but sufficiently distanced from where the two teeth meet or cometo a point (or the separation between the two teeth narrows) within aninterproximal area between the two teeth.

The collection of sample points provides a plurality of points in space(not in the same plane) that can be used to generate an average planeand a vector that is normal to the average plane. Sample points that areassociated with gingival curve portions can then be projected onto theaverage plane to generate two new curves. To minimize weakening of aregion of the aligner material within the interproximal area, themodified dynamic curve can be configured with an offset adjustment thatcomprises a minimum radius setting in the interproximal area to preventbreakage of the aligner material during use. The offset adjustment isfurther configured to ensure that a resulting cut line have a sufficientradius in the interproximal area to facilitate enough resistance forceapplied to the teeth to cause effective movement, but not too smallradius as to facilitate breakage. For example, a sharp point or othernarrow portion of material can create a stress region susceptible tobreak during use, and so should be avoided. Accordingly, rather thanhave the cut line comprise a sharp point or other narrow region, aplurality of intersection points and tangent points may be used togenerate a cut line in the interproximal region between adjacent teeththat maintains structural strength of the aligner and prevents sharppoints and/or narrow portions that could break. In one embodiment, thecut line is spaced apart from the gingival surface at regions where thealigner will contact a tooth and is designed to at least partially toucha patient's gingival surface in one or more interproximal regionsbetween teeth.

At block 110, processing logic determines one or more markings and/orelements that will mark the cut line in the aligner. A marking in thealigner may be a visible indicator in the aligner for a cut line, wherethe visible indicator does not alter a shape or feel of the aligner. Anelement in the aligner that marks the cut line may be a positive ornegative protrusion that does affect the shape of the aligner. Markingsmay remain in the aligner without affecting a fit of the aligner or afeel of the aligner when it is worn by a patient. However, elementsadded to the aligner may affect a fit and/or feel of the aligner unlesstrimmed off of the aligner.

Different types of markings may be determined for the cut line. Someexamples of markings include shapes such as arrows, triangles, lines,etc. that point to a cut line. For example, the tips of the shapes(e.g., the tips of arrows) may mark the cut line. Other examples ofmarkings include dashed or continuous lines. For example, a marking fora cut line may be a single line that a technician will cut along. Inanother example, a marking for a cut line may be two parallel lines,where a technician will cut between the two parallel lines. Other typesof markings are also possible. Additionally, multiple different types ofmarkings may be used to mark a single cut line. For example, a cut linemight be marked by a combination of a first marking of a line andadditional markings of arrows that point to the line.

In one embodiment, to define the markings to be used to show the cutline, processing logic determines a surface area on the aligner that isavailable for the markings. If there is a large surface area available,more markings may be used and/or larger markings may be used.Additionally, if there is a small amount of available surface area onthe aligner, fewer markings may be used and/or smaller markings may beused. Moreover, the types of markings to be used may be limited if thereis less than a threshold amount of available surface area on thealigner. For example, if shapes that point to the cut line are used tomark the cut line, then more shapes are generally used for sharpercurves. If there is insufficient space on an aligner to include themultiple shapes, then an alternative form of marking such as a singleline or pair of lines may be used.

At block 115, processing logic may determine an initial shape for a moldof the patient's dental arch at a treatment stage based on the digitalmodel of the dental arch at that treatment stage. Processing logic mayadditionally determine one or more features to add to the mold that willcause the aligner formed over the mold to have the determined markingsand/or elements. For example, one or more ridges or trenches may beadded to the mold that will cause one or more lines to form in thealigner formed over the mold. The ridges and/or trenches may have a verysmall height/depth and/or thickness, such that the ridges and/ortrenches will cause light to reflect off of and/or refract through thealigner formed over the mold in such a way to show the one or morelines. Similarly, other very shallow features having the shapes that areto be imprinted into the aligner may be added to the digital model forthe mold. These features may cause the aligner formed over the mold toinclude the markings without affecting a shape and/or feel of thealigner.

For elements that are to be added to the aligner, the correspondingfeatures added to the mold may have a depth, height and/or thicknessthat will affect a shape and/or feel of the aligner. Thus, the featuresfor the elements are generally larger, thicker, deeper, etc. than thefeatures for the markings. For example, a feature may be a trench orridge that will cause a perceptible ridge or trench in the aligner. Thisridge or trench in the aligner may be felt, and may be deep enough (ortall enough) to guide the movement of a blade in the hands of anoperator.

At block 120, processing logic determines whether additional cut lineinformation will be added to the aligner. As described above, theprimary cut line defines a distance between an edge of the aligner and agingival surface of a patient. The additional cut line may be for anyother cuts, such as cutouts in the aligner. For example, an additionalcut line may indicate an additional portion of the aligner to be removedsuch as for an occlusal surface of the aligner. Removal of the occlusalsurface of the aligner for one or more teeth may enable contact betweenthose teeth and teeth from an opposing dental arch. The additional cutline may also provide a cut out for one or more attachments on apatient's teeth (e.g., small, medium and/or large bumps, protrusions,wings, etc. that may be formed from a hard composite material thatadheres to the patient's teeth). The additional cut line may also be acut out to create a hook to be formed in the aligner, where the hook isusable with an elastic to apply additional forces to the patient'steeth. The additional cut line may also be for a cut out in the buccalsurface of the aligner to improve patient comfort and/or to satisfyfunctional parameters. Other secondary cut lines may also be determined,such as to make a cut in the aligner for other purposes (e.g., torelieve a strength or rigidity of the aligner or to generate space forattachments on the aligner). In some instances, a cut may not removematerial from the aligner.

If at block 110 it is determined that additional cut line information isto be added to the mold, the method returns to block 105, and theadditional cut line is determined. If no additional cut line informationis to be added to the mold, the method continues to block 125.

At block 125, processing logic determines whether additional informationis to be added to the aligner. The additional information may be anyinformation that pertains to the aligner. Examples of such additionalinformation includes a patient name, a patient identifier, a casenumber, a sequence identifier (e.g., indicating which aligner aparticular liner is in a treatment sequence), a date of manufacture, aclinician name, a logo and so forth.

Other additional information to add may be coordinate system referencemarks usable to orient a coordinate system of a trimming machine (e.g.,a laser trimming machine or a computer numerical control (CNC) machine)with a predetermined coordinate system of the aligner. By aligning thecoordinate system of the trimming machine to the coordinate system ofthe aligner, an accuracy of computer controlled trimming of the alignerat the cut line may be improved. In one embodiment, the markings for thecut line act as the coordinate system reference marks. Alternatively,the coordinate system reference marks may be different than the markingsfor the cut line. If coordinate system reference marks are to be usedthat are different from the markings for the cut line, and the aligneris to be trimmed by a CNC or other computer controlled trimming machine,then the markings for the cut line may be omitted. Accordingly, in somesuch embodiments method 100 may skip the operations of blocks 110-120.

If additional information is to be added, the method continues to block130. Otherwise the method proceeds to block 140.

At block 130, processing logic identifies the additional informationthat is relevant to the aligner and that is to be added to the aligner.At block 135, processing logic determines one or more additionalfeatures to add to the mold that will cause the aligner formed over themold to have the additional information. For example, the additionalfeatures may be raised alphanumeric characters on the mold with athickness and/or character width that is large enough to cause a visiblemarking on the aligner but small enough so as not to affect a shapeand/or feel of the aligner.

At block 140, processing logic may determine a final shape for the moldand may generate a digital model of the mold. Alternatively, the digitalmodel may have already been generated. In such an instance, processinglogic updates the already generated digital model to include thedetermined features for the mold. The digital model may be representedin a file such as a computer aided drafting (CAD) file or a 3D printablefile such as a stereolithography (STL) file. At block 145, the digitalmodel for the mold may be sent to a third party. The digital model mayinclude instructions that will control a fabrication system or device inorder to produce the mold with specified geometries. That third partymay then use the digital model to generate the mold having the addedfeatures.

FIG. 1B illustrates a flow diagram for a method 150 of trimming a shellusing cut line markings imprinted in the shell, in accordance with oneembodiment. Method 150 may be performed, for example, by a laboratory orclinician office.

At block 155 of method 100, a clinician office, laboratory, or otherentity receives a digital model of a mold, the digital model having beencreated as set forth in method 100. At block 160, the entity inputs thedigital model into a rapid prototyping machine. The rapid prototypingmachine then manufactures the mold using the digital model. One exampleof a rapid prototyping manufacturing machine is a 3D printer. 3DPrinting includes any layer-based additive manufacturing processes. 3Dprinting may be achieved using an additive process, where successivelayers of material are formed in proscribed shapes. 3D printing may beperformed using extrusion deposition, granular materials binding,lamination, photopolymerization, continuous liquid interface production(CLIP), or other techniques. 3D printing may also be achieved using asubtractive process, such as milling.

In one embodiment, stereolithography (SLA), also known as opticalfabrication solid imaging, is used to fabricate an SLA mold. In SLA, themold is fabricated by successively printing thin layers of aphoto-curable material (e.g., a polymeric resin) on top of one another.A platform rests in a bath of a liquid photopolymer or resin just belowa surface of the bath. A light source (e.g., an ultraviolet laser)traces a pattern over the platform, curing the photopolymer where thelight source is directed, to form a first layer of the mold. Theplatform is lowered incrementally, and the light source traces a newpattern over the platform to form another layer of the mold at eachincrement. This process repeats until the mold is completely fabricated.Once all of the layers of the mold are formed, the mold may be cleanedand cured.

Materials such as a polyester, a co-polyester, a polycarbonate, apolycarbonate, a thermoplastic polyurethane, a polypropylene, apolyethylene, a polypropylene and polyethylene copolymer, an acrylic, acyclic block copolymer, a polyetheretherketone, a polyamide, apolyethylene terephthalate, a polybutylene terephthalate, apolyetherimide, a polyethersulfone, a polytrimethylene terephthalate, astyrenic block copolymer (SBC), a silicone rubber, an elastomeric alloy,a thermoplastic elastomer (TPE), a thermoplastic vulcanizate (TPV)elastomer, a polyurethane elastomer, a block copolymer elastomer, apolyolefin blend elastomer, a thermoplastic co-polyester elastomer, athermoplastic polyamide elastomer, or combinations thereof, may be usedto directly form the mold. The materials used for fabrication of themold can be provided in an uncured form (e.g., as a liquid, resin,powder, etc.) and can be cured (e.g., by photopolymerization, lightcuring, gas curing, laser curing, crosslinking, etc.). The properties ofthe material before curing may differ from the properties of thematerial after curing.

At block 165, the aligner is formed over the mold. The formed alignerincludes the markings and/or elements that mark the one or more cutlines. The aligner may additionally include markings that provideadditional information, such as the patient name, case number, and soon. In one embodiment, a sheet of material is pressure formed orthermoformed over the mold. The sheet may be, for example, a sheet ofplastic (e.g., an elastic thermoplastic, a sheet of polymeric material,etc.). To thermoform the shell over the mold, the sheet of material maybe heated to a temperature at which the sheet becomes pliable. Pressuremay concurrently be applied to the sheet to form the now pliable sheetaround the mold with the features that will imprint the markings and/orelements in the aligner. Once the sheet cools, it will have a shape thatconforms to the mold. In one embodiment, a release agent (e.g., anon-stick material) is applied to the mold before forming the shell.This may facilitate later removal of the mold from the shell.

At block 175, the aligner is removed from the mold. At block 175, thealigner is then cut along the cut line (or cut lines) using the markingsand/or elements that were imprinted in the aligner. In one embodiment,the aligner is manually cut by a technician using scissors, a bur, acutting wheel, a scalpel, or any other cutting implement. If the cutline was marked using a single line, then the technician may cut alongthat line. If the cut line was marked using two lines that define theline, then the technician may cut between the two lines. If the cut linewas marked using a plurality of shapes that point to the cut line, thenthe technician may cut between the shapes. If multiple cut lines aremarked, then the technician may cut along each of the cut lines. In oneembodiment, a first cutting implement is used to cut along a first cutline and a second cutting implement is used to cut along a second cutline.

In another embodiment, the aligner is cut along the cut line by acomputer controlled trimming machine such as a CNC machine or a lasertrimming machine. The computer controlled trimming machine may include acamera that is capable of identifying the cut line in the aligner. Thecomputer controlled trimming machine may use images from the camera todetermine a location of the cut line from markings in the aligner, andmay control an angle and position of a cutting tool of the trimmingmachine to trim the aligner along the cut line using the identifiedmarkings.

Additionally, or alternatively, the aligner may include coordinatesystem reference marks usable to orient a coordinate system of thetrimming machine with a predetermined coordinate system of the aligner.The trimming machine may receive a digital file with trimminginstructions (e.g., that indicate positions and angles of a laser orcutting tool of the trimming machine to cause the trimming machine totrim the aligner along the cut line). By aligning the coordinate systemof the trimming machine to the aligner, an accuracy of computercontrolled trimming of the aligner at the cut line may be improved. Thecoordinate system reference marks may include marks sufficient toidentify an origin and an x, y and z axis.

In one embodiment, prior to trimming the aligner a technician may applya dye, a colored filler, or other material to the aligner to fill inslight indentations left by one or more elements imprinted in thealigner. The dye, colored filler, etc. may color the slight indentationswithout coloring a remainder of the aligner. This may increase acontrast between the cut line and the remainder of the aligner.

FIG. 2A illustrates a flow diagram for a method 200 of fabricating amold with cut line markings for a shell formed over the mold, inaccordance with one embodiment. These cut line markings will not betransferred to the aligner formed over the mold. Because the alignermaterial is transparent, the markings can be seen through the alignerwhile the aligner is physically positioned on the shell. One or moreoperations of method 200 are performed by processing logic of acomputing device. The processing logic may include hardware (e.g.,circuitry, dedicated logic, programmable logic, microcode, etc.),software (e.g., instructions executed by a processing device), firmware,or a combination thereof. For example, one or more operations of method200 may be performed by a processing device executing a computer aideddrafting (CAD) program or module such as model generator 650 of FIG. 6 .

At block 202 of method 200, a shape of a mold and/or of a dental arch ata treatment stage is determined. In one embodiment, the shape isdetermined based on a scan of an object to be modeled (e.g., anintraoral scan of a patient's upper and/or lower dental arches asdiscussed above with reference to block 102 of method 100. Once theshape of a mold is determined, processing logic may perform operationsto add cut line information to that mold, as set forth below.Alternatively, a shape of a dental arch may be determined, cut lineinformation may be determined for an aligner, and then a shape for amold may be determined after the cut line information is determined.

At block 205, processing logic determines a customized cut line for analigner to be formed over the shell. The cut line may be a gingival cutline that represents an interface between an aligner and a patient'sgingiva, as discussed above. The cut line may be determined as set forthwith reference to method 100.

At block 210, processing logic determines one or more markings and/orfeatures to add to the mold over which an aligner will be formed thatwill cause the cut line to be visible while the aligner is on the mold.A marking in the mold may be a visible indicator for a cut line, wherethe visible indicator does not alter a shape of the mold. Differenttypes of markings may be determined for the cut line. Some examples ofmarkings include shapes such as arrows, triangles, lines, etc. thatpoint to a cut line. For example, the tips of the shapes (e.g., the tipsof arrows) may mark the cut line. Other examples of markings includedashed or continuous lines. For example, a marking for a cut line may bea single line that a technician will cut along. In another example, amarking for a cut line may be two parallel lines, where a technicianwill cut between the two parallel lines. Other types of markings arealso possible. Other examples of markings include an interface betweentwo different materials and/or colors. For such an example, determiningthe markings and/or features to add to the mold includes determining afirst portion of the mold to be manufactured using at least one of afirst material or a first color and a second portion of the mold to bemanufactured using at least one of a second material or a second color.An interface between the first portion of the mold and the secondportion of the mold may define the cut line. Additionally, multipledifferent types of markings may be used to mark a single cut line.

At block 212, processing logic determines whether any additional cutline information for one or more additional cut lines is to be added tothe mold and/or to the aligner that will be formed over the mold. Ifadditional cut line is to be added, the method continues to block 215.If no additional cut line is to be added, the method proceeds to block225.

At block 215, processing logic determines one or more additional cutlines for the aligner. The additional cut lines may be for cutouts inthe aligner, to expose an occlusal surface, to expose an attachment on atooth, to provide a point to secure an elastic and/or for other purposesdiscussed herein.

At block 218, processing logic determines one or more markings and/orelements in the aligner that will mark the one or more additional cutlines on the aligner. Alternatively, processing logic may determine oneor more additional features in the mold that will cause markings for theone or more additional cut lines to be visible in the aligner while thealigner is on the mold.

In one embodiment, at block 220 processing logic determines one or morefeatures to add to the mold that will cause the aligner formed over themold to have the determined markings and/or elements, as discussed withreference to method 100. If all of the additional cut lines will beshown only in the mold and not in the aligner, then the operations ofblock 220 may be skipped.

At block 225, processing logic determines whether additional informationis to be added to the aligner. The additional information may be anyinformation that pertains to the aligner. Examples of such additionalinformation includes a patient name, a patient identifier, a casenumber, a sequence identifier (e.g., indicating which aligner aparticular liner is in a treatment sequence), a date of manufacture, aclinician name, a logo and so forth. If additional information is to beadded, the method continues to block 230. Otherwise the method proceedsto block 240.

At block 230, processing logic identifies the additional informationthat is relevant to the aligner and that is to be added to the aligner.At block 235, processing logic determines one or more additionalfeatures to add to the mold that will cause the aligner formed over themold to have the additional information. For example, the additionalfeatures may be raised alphanumeric characters on the mold with athickness and/or character width that is large enough to cause a visiblemarking on the aligner but small enough so as not to affect a shapeand/or feel of the aligner.

At block 240, processing logic generates a digital model of the mold.Alternatively, the digital model may have already been generated. Insuch an instance, processing logic updates the already generated digitalmodel to include the determined features for the mold. The digital modelmay be represented in a file such as a computer aided drafting (CAD)file or a 3D printable file such as a stereolithography (STL) file. Atblock 245, the digital model for the mold may be sent to a third party.That third party may then use the digital model to generate the moldhaving the added features.

FIG. 2B illustrates a flow diagram for a method 250 of trimming a shellusing cut line markings in a mold over which the shell is formed, inaccordance with one embodiment. Method 250 may be performed, forexample, by a laboratory or clinician office.

At block 255 of method 200, a clinician office, laboratory, or otherentity receives a digital model of a mold, the digital model having beencreated as set forth in method 200. At block 260, the entity inputs thedigital model into a rapid prototyping machine. The rapid prototypingmachine then manufactures the mold using the digital model. One exampleof a rapid prototyping manufacturing machine that may be used is a 3Dprinter. 3D printing may be performed using extrusion deposition,granular materials binding, lamination, photopolymerization, or othertechniques.

Materials such as a polyester, a co-polyester, a polycarbonate, apolycarbonate, a thermoplastic polyurethane, a polypropylene, apolyethylene, a polypropylene and polyethylene copolymer, an acrylic, acyclic block copolymer, a polyetheretherketone, a polyamide, apolyethylene terephthalate, a polybutylene terephthalate, apolyetherimide, a polyethersulfone, a polytrimethylene terephthalate, astyrenic block copolymer (SBC), a silicone rubber, an elastomeric alloy,a thermoplastic elastomer (TPE), a thermoplastic vulcanizate (TPV)elastomer, a polyurethane elastomer, a block copolymer elastomer, apolyolefin blend elastomer, a thermoplastic co-polyester elastomer, athermoplastic polyamide elastomer, or combinations thereof, may be usedto directly form the mold. The materials used for fabrication of themold can be provided in an uncured form (e.g., as a liquid, resin,powder, etc.) and can be cured (e.g., by photopolymerization, lightcuring, gas curing, laser curing, crosslinking, etc.). The properties ofthe material before curing may differ from the properties of thematerial after curing.

Optionally, the rapid prototyping techniques described herein allow forfabrication of a mold including multiple materials, referred to hereinas “multi-material direct fabrication.” In some embodiments, amulti-material direct fabrication method involves concurrently formingan object from multiple materials in a single manufacturing step. Forinstance, a multi-tip extrusion apparatus can be used to selectivelydispense multiple types of materials (e.g., resins, liquid, solids, orcombinations thereof) from distinct material supply sources in order tofabricate an object from a plurality of different materials.Alternatively or in combination, a multi-material direct fabricationmethod can involve forming an object from multiple materials in aplurality of sequential manufacturing steps. For instance, a firstportion of the object (e.g., a main portion of the mold) can be formedfrom a first material in accordance with any of the direct fabricationmethods herein, then a second portion of the object (e.g., one or moremarkings on the mold that show the cut line) can be formed from a secondmaterial in accordance with methods herein, and so on, until theentirety of the object has been formed. The relative arrangement of thefirst and second portions can be varied as desired. In one embodiment,multi-material direct fabrication is used to cause a first material tobe used for the markings of the cut line on the mold, and to cause oneor more additional materials to be used for the remainder of the mold.

At block 265, the aligner is formed over the mold, such as by pressureforming or thermoforming. At block 270, the aligner is manually cutalong the one or more cut lines using the markings and/or features inthe mold as a guide. The aligner may be cut or trimmed using cuttingequipment such as a burr, a wheel saw, a scalpel, and so on.

At block 275, the aligner is removed from the mold. At block 280, adetermination is made as to whether the aligner includes any markingsand/or elements that show one or more additional cut lines. If so, themethod continues to block 285. Otherwise the method ends.

At block 285, the aligner is then manually cut (e.g., by a technician)along the cut line (or cut lines) using the markings and/or elementsthat were imprinted in the aligner. The aligner may be cut usingscissors, a bur, a cutting wheel, a scalpel, or any other cuttingimplement. In one embodiment, a first cutting implement (e.g., a burr,wheel saw or scalpel) is used to cut along a first cut line at block 270and a second cutting implement (e.g., scissors) is used to cut along asecond cut line at block 285. The aligner may additionally includemarkings that provide additional information, such as the patient name,case number, and so on.

In one embodiment, prior to trimming the aligner at block 285 atechnician may apply a dye, a colored filler, or other material to thealigner to fill in slight indentations left by one or more elementsimprinted in the aligner. The dye, colored filler, etc. may color theslight indentations without coloring a remainder of the aligner. Thismay increase a contrast between the cut line and the remainder of thealigner.

In the embodiments so far described, aligners and other shells areindirectly fabricated by first fabricating a mold, and then forming thealigner or other shell over the mold. In some embodiments, shells suchas aligners may be directly fabricated using rapid prototypingtechniques and a digital model of the aligner or other shell. Forexample, shells may be produced using direct fabrication, such asadditive manufacturing techniques (e.g., 3D printing) or subtractivemanufacturing techniques (e.g., milling). Direct fabrication of analigner may involve forming the aligner without using a physical mold todefine a geometry of the aligner. Some examples of rapid prototypingtechniques include photopolymerization (e.g., stereolithograpy),material jetting (in which material is jetted onto a build platformusing either a continuous or drop on demand approach), binder jetting(in which alternating layers of a build material and a binding materialare deposited by a print head), fused deposition modeling, powder bedfusion, sheet lamination, and so on.

FIG. 3 illustrates a flow diagram for a method 300 of directlyfabricating an aligner or other shell with cut line markings, inaccordance with one embodiment. One or more operations of method 300 areperformed by processing logic of a computing device. The processinglogic may include hardware (e.g., circuitry, dedicated logic,programmable logic, microcode, etc.), software (e.g., instructionsexecuted by a processing device), firmware, or a combination thereof.For example, one or more operations of method 300 may be performed by aprocessing device executing a computer aided drafting (CAD) program ormodule such as model generator 650 of FIG. 6 .

At block 302 of method 300, processing logic determines a shape for analigner. In one embodiment, the shape is determined based on a scan ofan object to be modeled. In the example of orthodontics, an intraoralscan of a patient's dental arch may be performed to generate a threedimensional (3D) virtual model of the patient's dental arch. In otherapplications, virtual 3D models may also be generated based on scans ofan object to be modeled or based on use of computer aided draftingtechniques (e.g., to design the virtual 3D mold). Alternatively, aninitial negative mold may be generated from an actual object to bemodeled. The negative mold may then be scanned to determine a shape of apositive mold that will be produced.

Referring back to the example of orthodontics, multiple differentdigital models of a patient's dental arch and/or teeth may be generated.A first digital model may be a model of a patient's dental arch and/orteeth as they presently exist, and a final digital model may be a modelof the patient's dental arch and/or teeth after correction of one ormore teeth and/or a jaw. Multiple intermediate digital models may alsobe generated, each of which may be incrementally different from previousdigital models. For each digital model of a dental arch and/or teeth, acorresponding digital model of an aligner that fits over the dental archand/or teeth is also generated. A separate digital model may begenerated for each aligner. Each digital model of an aligner may be a 3Dvirtual model that represents an aligner to be used to reposition apatient's teeth at a particular phase of treatment.

At block 305, processing logic determines one or more cut lines for analigner. As set forth above, a cut line may define an interface betweenan edge of the aligner and a gingival line of the patient. A cut linemay additionally or alternatively define one or more cut outs for thealigner, such as to expose an occlusal surface of a tooth, to expose anattachment to a tooth, to provide an anchor point for an elastic, and soon.

At block 310, processing logic determines one or more markings and/orelements to be added to the aligner to mark the one or more cut lines.The markings may be a single line (e.g., that will be cut along), a pairof lines (e.g., where a technician will cut between the lines), aplurality of shapes that point to the cut line, and so on. The markingsmay be produced by using a first material and/or color for the markingsand a second material and/or color for a remainder of the aligner.Accordingly, determining the markings may include determining whichportions of the aligner will be manufactured with a first color and/ormaterial, and which portions of the aligner will be manufactured with asecond color and/or material. Alternatively, the markings may beproduced by adjusting a shape of the aligner. The shape may be adjustedenough to cause a marking, but not enough to cause a shape adjustmentthat can be felt. Alternatively, the shape may be adjusted by causingthe aligner to be thinner or thicker at the area of the markings. Forexample, the shape may be adjusted to include a trench or ridge thatfollows the cut line. The shape may also be adjusted to add aperforation along the cut line.

Materials such as a polyester, a co-polyester, a polycarbonate, apolycarbonate, a thermoplastic polyurethane, a polypropylene, apolyethylene, a polypropylene and polyethylene copolymer, an acrylic, acyclic block copolymer, a polyetheretherketone, a polyamide, apolyethylene terephthalate, a polybutylene terephthalate, apolyetherimide, a polyethersulfone, a polytrimethylene terephthalate, astyrenic block copolymer (SBC), a silicone rubber, an elastomeric alloy,a thermoplastic elastomer (TPE), a thermoplastic vulcanizate (TPV)elastomer, a polyurethane elastomer, a block copolymer elastomer, apolyolefin blend elastomer, a thermoplastic co-polyester elastomer, athermoplastic polyamide elastomer, or combinations thereof, may be usedto directly form the aligner. The materials used for direct fabricationcan be provided in an uncured form (e.g., as a liquid, resin, powder,etc.) and can be cured (e.g., by photopolymerization, light curing, gascuring, laser curing, crosslinking, etc.). The properties of thematerial before curing may differ from the properties of the materialafter curing. Once cured, the materials herein can exhibit sufficientstrength, stiffness, durability, biocompatibility, etc. for use in thealigner. The post-curing properties of the materials used can beselected according to the desired properties for the correspondingportions of the aligner.

In some embodiments, relatively rigid portions of the aligner can beformed via direct fabrication using one or more of the followingmaterials: a polyester, a co-polyester, a polycarbonate, a thermoplasticpolyurethane, a polypropylene, a polyethylene, a polypropylene andpolyethylene copolymer, an acrylic, a cyclic block copolymer, apolyetheretherketone, a polyamide, a polyethylene terephthalate, apolybutylene terephthalate, a polyetherimide, a polyethersulfone, and/ora polytrimethylene terephthalate. In some embodiments, relativelyelastic portions of the aligner can be formed via direct fabricationusing one or more of the following materials: a styrenic block copolymer(SBC), a silicone rubber, an elastomeric alloy, a thermoplasticelastomer (TPE), a thermoplastic vulcanizate (TPV) elastomer, apolyurethane elastomer, a block copolymer elastomer, a polyolefin blendelastomer, a thermoplastic co-polyester elastomer, and/or athermoplastic polyamide elastomer.

Optionally, the direct fabrication methods described herein allow forfabrication of an aligner including multiple materials, referred toherein as “multi-material direct fabrication.” In some embodiments, amulti-material direct fabrication method involves concurrently formingan object from multiple materials in a single manufacturing step. Forinstance, a multi-tip extrusion apparatus can be used to selectivelydispense multiple types of materials (e.g., resins, liquid, solids, orcombinations thereof) from distinct material supply sources in order tofabricate an object from a plurality of different materials.Alternatively or in combination, a multi-material direct fabricationmethod can involve forming an object from multiple materials in aplurality of sequential manufacturing steps. For instance, a firstportion of the object (e.g., a body of the aligner) can be formed from afirst material in accordance with any of the direct fabrication methodsherein, then a second portion of the object (e.g., markings for a cutline) can be formed from a second material in accordance with methodsherein, and so on, until the entirety of the object has been formed. Therelative arrangement of the first and second portions can be varied asdesired, e.g., the first portion can be partially or wholly encapsulatedby the second portion of the object. In one embodiment, multi-materialdirect fabrication is used to cause a first material to be used for themarkings of the cut line on the aligner, and to cause one or moreadditional materials to be used for the remainder of the aligner.

At block 315, processing logic determines whether additional informationis to be added to the aligner. The additional information may be anyinformation that pertains to the aligner. Examples of such additionalinformation include a patient name, a patient identifier, a case number,a sequence identifier (e.g., indicating which aligner a particular lineris in a treatment sequence), a date of manufacture, a clinician name, alogo and so forth. If additional information is to be added, the methodcontinues to block 320. Otherwise the method proceeds to block 330.

At block 320, processing logic identifies the additional informationthat is relevant to the aligner and that is to be added to the aligner.At block 325, processing logic determines one or more additionalmarkings to add to the aligner that will cause the aligner to have orprovide the additional information. For example, the additional markingsmay be alphanumeric characters on the aligner.

At block 330, processing logic generates a digital model of the aligner.Alternatively, the digital model may have already been generated. Insuch an instance, processing logic updates the already generated digitalmodel to include the determined markings and/or elements. The digitalmodel may be represented in a file such as a computer aided drafting(CAD) file or a 3D printable file such as a stereolithography (STL)file. At block 335, the digital model for the aligner may be sent to athird party. That third party may then use the digital model to generatethe aligner, and may then trim the aligner using the markings and/orelements formed in the aligner.

FIG. 4A illustrates a mold 400 of a dental arch with markings 420 thatpoint to a cut line 415 (also referred to as a trimming line) for ashell formed over the mold 400. The markings 420 are triangles thatpoint to the cut line 415. The markings 420 have been formed in the mold400 using at least one of a different material or a different color thanthe material and/or color used to manufacture a remainder of the mold400.

FIG. 4B illustrates a mold 430 of a dental arch with markings 445 thatshow a cut line 440 for a shell formed over the mold 400, in accordancewith another embodiment. As shown, the markings 445 include a singleline that has been formed in the mold 430 using at least one of adifferent material or a different color than the material and/or colorused to manufacture a remainder of the mold 430.

FIG. 4C illustrates a mold 480 of a dental arch with features 482 thatwill cause a shell formed over the mold 480 to have cut line markings,in accordance with one embodiment. The features 482 include a singleshallow ridge or trench in the illustrated example. As shown, thefeatures 482 include a curved line that roughly follows a gingival lineof the dental arch.

FIG. 4D illustrates a mold 484 of a dental arch with features 486 thatwill cause a shell formed over the mold 484 to have cut line markings,in accordance with another embodiment. The features 486 include a singleshallow ridge or trench in the illustrated example. As shown, thefeatures 486 include an approximately straight line along the dentalarch.

FIG. 4E illustrates a mold 490 of a dental arch with features 492 thatwill cause a shell formed over the mold 490 to have cut line markingsthat follow a cut line 494, in accordance with another embodiment. Asshown, the features 492 are triangles that point to the cut line 494.

FIG. 5 illustrates an example orthodontic aligner 505 worn by a person.An edge 502 of the orthodontic aligner 505 has a wavy shape in which thealigner 505 is away from (or under) the gum line 515 where the aligner505 touches a tooth and on (or over) the gum line 510 in theinterproximal regions between adjacent teeth.

FIG. 6 illustrates a diagrammatic representation of a machine in theexample form of a computing device 600 within which a set ofinstructions, for causing the machine to perform any one or more of themethodologies discussed with reference to the methods of FIGS. 1A, 2Aand 3 . In alternative embodiments, the machine may be connected (e.g.,networked) to other machines in a Local Area Network (LAN), an intranet,an extranet, or the Internet. For example, the machine may be networkedto a rapid prototyping apparatus such as a 3D printer or SLA apparatus.The machine may operate in the capacity of a server or a client machinein a client-server network environment, or as a peer machine in apeer-to-peer (or distributed) network environment. The machine may be apersonal computer (PC), a tablet computer, a set-top box (STB), aPersonal Digital Assistant (PDA), a cellular telephone, a web appliance,a server, a network router, switch or bridge, or any machine capable ofexecuting a set of instructions (sequential or otherwise) that specifyactions to be taken by that machine. Further, while only a singlemachine is illustrated, the term “machine” shall also be taken toinclude any collection of machines (e.g., computers) that individuallyor jointly execute a set (or multiple sets) of instructions to performany one or more of the methodologies discussed herein.

The example computing device 600 includes a processing device 602, amain memory 604 (e.g., read-only memory (ROM), flash memory, dynamicrandom access memory (DRAM) such as synchronous DRAM (SDRAM), etc.), astatic memory 606 (e.g., flash memory, static random access memory(SRAM), etc.), and a secondary memory (e.g., a data storage device 628),which communicate with each other via a bus 608.

Processing device 602 represents one or more general-purpose processorssuch as a microprocessor, central processing unit, or the like. Moreparticularly, the processing device 602 may be a complex instruction setcomputing (CISC) microprocessor, reduced instruction set computing(RISC) microprocessor, very long instruction word (VLIW) microprocessor,processor implementing other instruction sets, or processorsimplementing a combination of instruction sets. Processing device 602may also be one or more special-purpose processing devices such as anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA), a digital signal processor (DSP), network processor,or the like. Processing device 602 is configured to execute theprocessing logic (instructions 626) for performing operations and stepsdiscussed herein.

The computing device 600 may further include a network interface device622 for communicating with a network 664. The computing device 600 alsomay include a video display unit 610 (e.g., a liquid crystal display(LCD) or a cathode ray tube (CRT)), an alphanumeric input device 612(e.g., a keyboard), a cursor control device 614 (e.g., a mouse), and asignal generation device 620 (e.g., a speaker).

The data storage device 628 may include a machine-readable storagemedium (or more specifically a non-transitory computer-readable storagemedium) 624 on which is stored one or more sets of instructions 626embodying any one or more of the methodologies or functions describedherein. A non-transitory storage medium refers to a storage medium otherthan a carrier wave. The instructions 626 may also reside, completely orat least partially, within the main memory 604 and/or within theprocessing device 602 during execution thereof by the computer device600, the main memory 604 and the processing device 602 also constitutingcomputer-readable storage media.

The computer-readable storage medium 624 may also be used to store oneor more virtual 3D models (also referred to as electronic models) and/ora mold generator 650, which may perform one or more of the operations ofmethods 100 and 200 described with reference to FIGS. 1A, 2A and 3 . Thecomputer readable storage medium 624 may also store a software librarycontaining methods that call a model generator 650. While thecomputer-readable storage medium 624 is shown in an example embodimentto be a single medium, the term “computer-readable storage medium”should be taken to include a single medium or multiple media (e.g., acentralized or distributed database, and/or associated caches andservers) that store the one or more sets of instructions. The term“computer-readable storage medium” shall also be taken to include anymedium that is capable of storing or encoding a set of instructions forexecution by the machine and that cause the machine to perform any oneor more of the methodologies of the present invention. The term“computer-readable storage medium” shall accordingly be taken toinclude, but not be limited to, solid-state memories, and optical andmagnetic media.

It is to be understood that the above description is intended to beillustrative, and not restrictive. Many other embodiments will beapparent upon reading and understanding the above description. Althoughembodiments of the present invention have been described with referenceto specific example embodiments, it will be recognized that theinvention is not limited to the embodiments described, but can bepracticed with modification and alteration within the spirit and scopeof the appended claims. Accordingly, the specification and drawings areto be regarded in an illustrative sense rather than a restrictive sense.The scope of the invention should, therefore, be determined withreference to the appended claims, along with the full scope ofequivalents to which such claims are entitled.

What is claimed is:
 1. A method comprising: generating or receiving, bya processing device, a digital three-dimensional model of a mold for adental arch of a patient; determining, by the processing device, a cutline for a shell that is to be formed over the mold for the dental archof the patient; and supplementing the digital three-dimensional model byadding an auxiliary structure to the digital three-dimensional model,wherein the auxiliary structure comprises at least one of an elevationor a depression that extends along the cut line and is in the digitalthree-dimensional model, wherein the auxiliary structure is designedsuch that the shell formed over the mold will have an impression of theauxiliary structure that identifies the cut line.
 2. The method of claim1, wherein the cut line is customized for the dental arch of thepatient.
 3. The method of claim 1, wherein the shell comprises at leastone of an orthodontic aligner, an orthodontic retainer or an orthodonticsplint to be used for at least one of aligning, retaining, orpositioning one or more teeth of a patient.
 4. The method of claim 1,wherein at least one of a) the elevation comprises a ridge or b) thedepression comprises a trench.
 5. The method of claim 1, furthercomprising: manufacturing the mold by a rapid prototyping machine usingthe digital three- dimensional model, the mold comprising the auxiliarystructure; thermoforming or pressure forming a plastic sheet over themold to form the shell, the shell comprising the impression of theauxiliary structure; and cutting the shell along the cut line using theimpression of the auxiliary structure.
 6. The method of claim 1, whereinthe cut line controls a distance between an edge of the shell and a gumline of a patient.
 7. The method of claim 1, further comprising:automatically determining the cut line and the auxiliary structure toadd to the digital three-dimensional model without user input.
 8. Themethod of claim 1, further comprising: determining a gingival line inthe digital three-dimensional model; and determining the cut line basedon the gingival line.
 9. A system comprising: a computing device havinga memory and a processing device operatively coupled to the memory, thecomputing device configured to: generate or receive a digitalthree-dimensional model of a mold for a dental arch of a patient;determine a cut line for a shell that is to be formed over the mold forthe dental arch of the patient; and supplement the digitalthree-dimensional model by adding an auxiliary structure to the digitalthree-dimensional model, wherein the auxiliary structure comprises atleast one of an elevation or a depression that extends along the cutline and is in the digital three-dimensional model, wherein theauxiliary structure is designed to cause the shell formed over the moldto have an impression of the auxiliary structure that identifies the cutline.
 10. The system of claim 9, wherein the cut line is customized forthe dental arch of the patient.
 11. The system of claim 9, wherein theshell comprises at least one of an orthodontic aligner, an orthodonticretainer or an orthodontic splint to be used for at least one ofaligning, retaining, or positioning one or more teeth of a patient. 12.The system of claim 9, wherein at least one of a) the elevationcomprises a ridge or b) the depression comprises a trench.
 13. Thesystem of claim 9, further comprising: a rapid prototyping machine tomanufacture the mold using the digital three- dimensional model, themanufactured mold comprising the auxiliary structure; a thermoformingmachine to thermoform a plastic sheet over the mold to form the shell,the shell comprising the impression of the auxiliary structure; and acutting machine to cut the shell along the cut line using the impressionof the auxiliary structure.
 14. The system of claim 9, wherein the cutline controls a distance between an edge of the shell and a gum line ofa patient.
 15. The system of claim 9, wherein the computing device isfurther configured to: automatically determine the cut line and theauxiliary structure to add to the digital three-dimensional modelwithout user input.
 16. The system of claim 9, wherein the computingdevice is further configured to: determine a gingival line in thedigital three-dimensional model; and determine the cut line based on thegingival line.
 17. A non-transitory computer readable medium comprisinginstructions that, when executed by a processing device, cause theprocessing device to perform operations comprising: generating orreceiving, by the processing device, a digital three-dimensional modelof a mold for a dental arch of a patient; determining, by the processingdevice, a cut line for a shell that is to be formed over the mold forthe dental arch of the patient; and supplementing the digitalthree-dimensional model by adding an auxiliary structure to the digitalthree-dimensional model, wherein the auxiliary structure comprises atleast one of an elevation or a depression that extends along the cutline and is in the digital three-dimensional model, wherein theauxiliary structure will cause the shell formed over the mold to have animpression of the auxiliary structure that identifies the cut line. 18.The non-transitory computer readable medium of claim 17, the operationsfurther comprising: automatically determining the cut line and theauxiliary structure to add to the digital three-dimensional modelwithout user input.
 19. The non-transitory computer readable medium ofclaim 17, the operations further comprising: determining a gingival linein the digital three-dimensional model; and determining the cut linebased on the gingival line.
 20. The non-transitory computer readablemedium of claim 17, wherein: the cut line is customized for the dentalarch of the patient; and the shell comprises at least one of anorthodontic aligner, an orthodontic retainer or an orthodontic splint tobe used for at least one of aligning, retaining, or positioning one ormore teeth of a patient.
 21. The non-transitory computer readable mediumof claim 17, wherein the cut line controls a distance between an edge ofthe shell and a gum line of a patient.